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Wireless and Fiber Optics

Who are we?

The optical research team engages in fiber optics, optical sensing, fiber lasers, optical beam outdoor and indoor propagation with respect to atmospheric influence on free-space optic (FSO) links and last but not least in visible light communication (VLC). Currently our scientific effort is focused on fundamental research as well as on cooperation with industry in the field of applied research.

Tamas Cseh, (Budapest University of Technology and Economics,Budapest), 2015

Svetlana Korsakova, (Saratov State University,Saratov), 2015

What are our research topics?

Our team research is focused on numerous areas of optical signal propagation and transmission.

First topic is represented by fiber optics, where we work on research and development of fiber sensors, fiber lasers, broadband optical signal generation and all-optical network components. We utilize state-of-art techniques and technologies. We test specialty optical fibers (microstructured, doped, special glass materials) for the purposes of liquid detection, nonlinear effects and supercontinuum generation. Furthermore we develop fiber pulsed fiber lasers, evaluate long-term effects on optical fibers, design fiber structures and much more. For these we utilize state-of-art simulation software and approaches. We work in co-operation with leading universities worldwide, Institute of Photonics and Electronics, Academy of Sciences and with a number of technological companies participating in the field of photonics.

Another research and development topic is represented by free-space optics (FSO), where we exploit several wireless optical links in the CTU campus connected into a simple network. We measure atmospheric parameters; we have a special turbulence chamber; we develop behavioral models of atmospheric turbulences, rain influence, etc. with respect to the quality of FSO links.

Last topic of interest is wireless optical communication inside buildings in visible light (indoor visible light communication, VLC), where transmissions over 7 Gbit/s have been achieved. Here our goal is analysis of LED technologies coverage as for room illumination and data transmission. Furthermore we test in international cooperation the employment of organic LED (OLED) for communication purposes..

What it is good for?

The optical fiber development in the last decades have enabled extreme growth in network transmission capacity, but also employment of optical fibers in other areas, such as eg. sensing. Optical fibers are isolants, they are chemically resistant and immune to electromagnetic interference – which makes the ideal candidates for sensing in hazardous environments. Special fiber structures then enable broadband signal generation, where application in medicine or chemical analysis is of overestimate value. Free-space optic link then enable high-speed transmission to numerous areas, where it is not possible to place optical fibers (historical town centers), or where standard high-speed transmissions are insufficient in capacity. Furthermore for VLC the LED illumination is massively applied worldwide not only indoor but also in public places. In contrast to radiofrequency region VLC provides several orders higher transmission speeds.

What have we been working on?

Fiber optic detection of liquids

The project is focused on development of fiber optical sensors with enhanced sensitivity for detection of liquid analytes. This detection is based on enhanced overlapping of evanescent wave with the liquid, in principle we speak of refractometric measurement. In the project we develop various types of fiber optic detection units for detection of liquid (such as hydrocarbons) not only based on silica fibers, but also based on microstructure optical fibers. This project is carried out in cooperation with SQS, Fiber optics.

Broadband optical source based on soft-glass fibers

Aim of the project is the development of a broadband optical source prototype (i.e. supercontinuum source). The supercontinuum source is composed of a pulsed laser and a nonlinear media – optical fiber. The nonlinear media is based in our application on conventional and microstructured optical soft-glass fibers (fluoride, lead-silicate, chalcogenide). In parallel we are developing a pulsed fiber laser at 1550 nm and 2000 nm. This project is carried out in cooperation with SQS, Fiber optics, development of the 2000 nm pulsed laser also in cooperation with Institute of photonics and electronics, AS CR.

Optical packet switch

Project aims at a switch development, which is based on optical packet routing. Main advantage stands in keeping the data payload in optical format, while only the label – IP address – is processed electronically. Employing this approach we achieve higher data speeds than with the consideration of opto-electronic speed limits. For the switching itself we utilize special fibers and nonlinear phenomena.

Femtosecond fiber laser

We develop fiber laser with passive mode synchronization, which exploits commercially available erbium-doped optical fiber and thanks to nonlinear polarization rotation in the loop, pulse behavior is achieved. It is possible to obtain pulses having full-width-at-half-maximum (FWHM) as short as 200fs, while preserving high energy. Our goal is the loop optimization and high repetition rate.

Microwave photonics

Unlike the conventional digital baseband transmission schemes supporting only one service at a time, the radio-over-fibre (RoF) transmission network enables the coexistence of multi-service and multi-operators in a shared resources, thereby offering increased link capacity, advanced networking (i.e., dynamic resources and allocations) without the need for frequency up-down conversion. An alternative option for fiber radio networks is to transmit the RF-based information over a free space opticaů (FSO) link in place of an optical fiber or combine these networks together. This leads to the bigger flexibility of the networks, which can bring reduced costs especially in dense urban areas. However, the link availability and performance quality is mostly affected by atmospheric weather conditions such as atmospheric turbulence, fog, rain, etc.

Optical fibers in harsh environment

The reliability of an optical communication system in a hazardous area may be adversely affected by temperature variation, pressure, humidity, high voltage transmission, radiation, etc.. In such conditions, optical fibers undergo structural changes that may result in their transmission characteristics being temporarily or permanently degraded. Thus it desires attention when the optical networks are designing going hand in hand with optical fiber networks growth. Our experiments are focused on crucial transmission parameters monitoring in long-term horizon.

Research of ambient influence on novel broadband free-space optical systems

Main aim of this project stands in national cooperation with partners of Cost project IC1101 OPTICWISE, which should lead to development of a new methodology for atmospheric parameters reconnaissance based on measurement of free-space optical systems utilizing adaptive approaches. Large measurement campaign including two optical links WaveBridge 500 by Plaintree, 4-beam optical wireless link FlightStrata G od LightPointe (1.25 Gbps, VCSEL at 850 nm) and approximately 400m long link MRV Telescope 700. Parallel measurement in microwave region (5GHz link Mikrotik) is being carried out, atmospheric parameters are being measured by two metrological stations and turbulent environment close to buildings is analyzed based on temperature gradient obtained by special sensor link and also based on radiometric noise temperature measurement. In analyses, the meteoradar database is utilized; containing rain intensity behavior in the area of 250x250km (Czech Republic) with 1km step and time step of 1min for a 3-year period.

Visible Light Communication (VLC)

In recent years, visible light communications (VLC) has rapidly gained interest among research communities worldwide. It is an emerging technology for future high capacity communication links utilizing the visible range of the electromagnetic spectrum (~370 – 780 nm), which is not only license free, but free from spectral overcrowding unlike radio frequencies (RF). VLC utilizes light-emitting diodes (LEDs), modulating them at high speeds that are much faster than the human eye can detect, to simultaneously provide data transmission and room illumination. A major challenge in VLC is the LED modulation bandwidths, which are limited to a few MHz. However, gigabit speed transmission links have already been demonstrated.

Concurrently, organic LEDs (OLEDs) have been the focus of enormous attention for solid-state lighting applications due to their advantages over conventional LEDs such as ultra-low costs, mechanical flexibility and large photoactive areas. As a result, researchers are starting to investigate the performance of OLEDs in VLC systems, which is a very challenging research area, as OLED bandwidths can be approximately three orders of magnitude lower than their LED counterparts. Our group works on development of such VLC links to drive both LEDs and OLEDs in order to implement broadcasting networks featuring advanced modulation formats such as orthogonal frequency division multiplexing (OFDM) or carrier-less amplitude and phase modulation (CAP). We have many international academic and industrial collaborations with world leading research groups in the field of VLC, including Northumbria University and University College London (UCL) or University of Bristol.